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Help with ECL/OBDII diagnosis

Ok, I'd like to request some guiding opinions on what all to look for on 3 different ECL/OBDII codes pulled today on my '96 OBW/2.5

A little background: Over the past couple of months, I've had the check engine light come on intermittantly, usually right after starting out first thing in the morning, sometimes right after filling the gas tank up. Sometime the ECL would blink for a few seconds, then turn solid, sometimes it would just come on solid. This does not happen all the time. And the ECL usually would turn off after driving another 70/80 miles. I've ignored it to this point because of the sporatic frequency of it coming on and then turning off and the car seems to run fine. My thinking was bad gas or an occassional hick-up with the ECU.

However, I just recently changed the fuel and air filters along with the PCV, and the ECL came back again today after starting out first thing this morning. I made the decision to finally do something about it and I drove to an AutoZone store which read and pulled the codes for me (free, and even provided me with printouts!!). So I've got these 3 codes along with these descriptions printed out from AutoZone:

1)

P0135, The PCM has determined that a malfunction exist in the heater circuit for oxygen sensor 1 in bank 1. (Oxygen sensor 1 is closest to the cylinder head before the catalytic converter, while oxygen sensor 2 & 3 are located further downstream and are typically mounted in or after the catalytic converter) (Bank 1 identifies the location of cylinder #1, while bank 2 identifies the cylinders on the opposite bank)

2)

P0304, The PCM had determined that a misfire has occurred in cylinder #4.

3)

P0420, The PCM had determined that the catalyst system efficiency for bank 1 is below threshold for the current engine operating conditions. (Bank 1 identifies the location of cylinder #1, while bank 2 indentifies the cylinders on the opposite bank)

So, I'll be for sure looking at the oxygen sensor(s). I replaced the O2 on the pre-cat about 50K miles ago, the car was at approx. 100K. There was no really reason to do so other than preventive maintenance. I still have the original O2 sensor and may throw that back on to see if there are any changes.

What about the misfire? Is it likely that these codes are all related to a single problem, or possible different problems that have occurred? What should I be checking for in addition to spark plug wire, ignition coil, plug boot tight on spark plug etc? BTW, The dealer put in new NGK platiums when the head gaskets where done at 138K. They said the wires and coil pack checked out fine.

I don't have my Haynes manual readily available at the moment - can anyone direct me to where the "heater circuit" for the oxygen sensor is located, and how to check it if possible?

This car now has 157K on her, and basically runs fine, good mpg, even when the ECL comes on.

My Acutron OBD II scanner works fine for receiving active codes that display when the check engine light is illuminated (u-check mode). I need to know how to use it for the read and memory modes. I have identified the green test mode connectors under the dash of my 1999 Legacy, but have not tried connecting them and using the scanner. Can anyone give my some guidance on the read and memory modes ? I have a sporatic problem on acceleration and don't get a check engine light and have done a complete tune up. The vehicle has 190,000.
fixitguy50

Hi fixitguy50 and to the board! This should probably be broken to a separate, new thread.

Did your reader come with instructions for any other modes it may have? Not all code readers can do freeze frame data. Many can read the code history of previous codes that set off the CEL/MIL. Connecting the green test mode connectors would not have anything to do with reading code history or freeze frame data. You could try reading live data values with the green test mode connectors connected, if the reader can do it.

Acceleration issues could be as simple as faulty knock sensor. For tune up, Soobs like NGK plugs and OEM plug wires. A good seafoaming of the intake might help, and cleaning the throttle body.

On the original topic. The CEL is flashing due to the missfire, this is probably going to be a tune up issue. I would check the plugs and wires and only replace with OE stuff. I would do the front O2 sensor before trying to address the 420 code. Once all of this is done erase the codes and drive it to see what pops back up. The moniters for Subys are way to picky for catalyst insuff. If the 420 comes back on get yourself a ong 18mm spark plug non fouler and drill out the center with a half inch bit and put it on between your downstream O2 and the pipe. I am running that setup on my 96 OB with no cat and no CEL!!

If the 420 comes back on get yourself a ong 18mm spark plug non fouler and drill out the center with a half inch bit and put it on between your downstream O2 and the pipe. I am running that setup on my 96 OB with no cat and no CEL!!

what's " a ong 18mm spark plug non fouler" ???

this sounds like what i need on my 95 leg w/ p0420 code, it comes and goes.

Hi fixitguy50 and to the board! This should probably be broken to a separate, new thread.

Did your reader come with instructions for any other modes it may have? Not all code readers can do freeze frame data. Many can read the code history of previous codes that set off the CEL/MIL. Connecting the green test mode connectors would not have anything to do with reading code history or freeze frame data. You could try reading live data values with the green test mode connectors connected, if the reader can do it.

Acceleration issues could be as simple as faulty knock sensor. For tune up, Soobs like NGK plugs and OEM plug wires. A good seafoaming of the intake might help, and cleaning the throttle body.

Hi fixitguy50 and to the board! This should probably be broken to a separate, new thread.

Did your reader come with instructions for any other modes it may have? Not all code readers can do freeze frame data. Many can read the code history of previous codes that set off the CEL/MIL. Connecting the green test mode connectors would not have anything to do with reading code history or freeze frame data. You could try reading live data values with the green test mode connectors connected, if the reader can do it.

Acceleration issues could be as simple as faulty knock sensor. For tune up, Soobs like NGK plugs and OEM plug wires. A good seafoaming of the intake might help, and cleaning the throttle body.

Tell me about seafoaming. What is it ? and how is it done ? I have noticed the intake manifold has excess deposits. Any tips regarding throttle body cleaning (engine speed, brand of cleaner) ?fixitguy50

A spark plug non fouler is basically a spacer used for cars that burn oil. It would normally thread on in between the spark plug and the head and has a small hole in the end to allow the spark to ignite the A/F mixture, but keeps the spark plug out of the combustion chamber. When using it on the O2 it sheilds the little vanes on the O2 from the exhaust and fools the ECU. I beleive the correct part number from motormite (Help products) is 42008 or something close to that.

Can you expand on the installation of the "Non Fouler" and what it's doing for you?

On the original topic. The CEL is flashing due to the missfire, this is probably going to be a tune up issue. I would check the plugs and wires and only replace with OE stuff. I would do the front O2 sensor before trying to address the 420 code. Once all of this is done erase the codes and drive it to see what pops back up. The moniters for Subys are way to picky for catalyst insuff. If the 420 comes back on get yourself a ong 18mm spark plug non fouler and drill out the center with a half inch bit and put it on between your downstream O2 and the pipe. I am running that setup on my 96 OB with no cat and no CEL!!

It is actually being done on alot of other makes as well. It is just a spacer really that kind of sheilds the D/S O2 from the exhaust stream. When mounted the vanes of the thimble on the O2 that sample the exhaust gases are almost covered, it fools the ECU into thinking that the cat is doing its job.

From my experience with my 2001 Forester 85k miles, you might be due for another front 02 sensor. Swap the old one back in if you are sure it still functions right. Cheap way to test. My front 02 sensors only lasted 40k miles each.